The invention relates to a synthetic biomaterial comprising a ceramic material. The biomaterial has a porous structure which makes it suitable for use as, for example, synthetic bone grafts. This allows it to be used in orthopedic surgery, including vertebrae repair, musculoskeletal reconstruction, fracture repair, hip and knee reconstruction, osseous augmentation procedures and oral/maxillofacial surgery.
Synthetic materials for bone grafts are usually made of calcium phosphate ceramics and have a porous structure similar to that of cancellous bone. Many are derived from animals or marine life, such as from bovine bone or coral. These are intended to offer an interconnected macroporous structure and provide intensive osteoconductivity to regenerate and heal the host bone tissue. However, many of these have problems because their precise composition and structure cannot be controlled.
Such synthetic bone grafts typically come with interconnected “macropores”, typically of 100-500 μm diameter. These provide a framework for the host bone to regenerate whilst reducing healing time. The pores allow bone tissue to grow into the bone graft. According to in vitro and in vivo experiments, the host's own bone tissue uses the macroporous structure to grow into the bone replacement material, the material being slowly degraded and being replaced by new bone growth. Ideally, biomaterials used for bone grafts should be microporous with a pore diameter of 1-10 μm. Such micropores have been found to improve the ability of osteoblasts and other cells from the host to bind to the synthetic biomaterial and to allow access of the cells to dissolve the sintered connections between the individual ceramic particles.
Typical commercially available synthetic bone grafts usually have a random distribution of pore sizes and no observable preferred orientation of the interconnected porous structure. Furthermore, they have little or no microporous structure.
For example, U.S. Pat. No. 6,511,510 discloses an osteoinductive biomaterial that is made from calcium phosphate or a glass ceramic. The material is stated to comprise micropores and macropores, the macropores preferably being interconnected. The micropores are only present on the surface of the material. The osteoinductive biomaterial is obtained by sintering a ceramic material. The material is preferably ground with sandpaper to remove chemical surface impurities and the material is then treated with an aqueous solution of an acid. The acid etches the surface of the material, especially the annealed particles' grains boundaries, to produce the micropores. Macropores may be formed using pore-forming agents such as hydrogen peroxide, baking powder or bicarbonate. Negative replica-forming agents such as wax or fiber are also disclosed which will not generate gas in the same way as hydrogen peroxide or baking powder, but will be burned to leave the same shape or pore as the original wax or fiber.
U.S. Pat. No. 6,479,418 discloses a method of preparing a porous ceramic body by mixing a slurry of a ceramic material with a viscous organic phase to obtain a dough, drying the dough and removing the organic phase by thermal decomposition. Foaming agents, such as sodium bicarbonate and citric acid may be used to create “macropores”. The surface of the ceramic body, including the surface of the pores, is stated to have a microporous surface. This is shown in the document as being irregular depressions in the surface of the material surrounded by irregular clumps of fused ceramic particles.
Ceramic materials used to mould natural objects are disclosed in U.S. Pat. No. 5,705,118. The ceramic uses gluten and/or a number of other materials as a binder. This is mixed together as a batch with water or other liquid, prior to spraying or applying onto an object to produce a mould. This is fired to produce a porous body.